1. Field of the Invention
The present invention relates generally to a Combined Circuit Switched (CS) call and Internet Protocol Multimedia Subsystem (IMS) session (hereinafter called CSI). In particular, the present invention relates to a method and apparatus for sending service information, which was changed due to a change of the state of a User Equipment (UE), to another peer entity connected to the UE.
2. Description of the Related Art
Circuit switching is used for typical voice service. The CS is a scheme in which a CS-based communication path is established between one user and another user. In comparison, IMS uses a packet-based variable communication path over IP, thus increasing transmission efficiency and ensuring stability. IMS supports a multiparty call as well as a one-to-one call.
Global System for Mobile communications (GSM) and Enhanced Data Rates GSM Evolution (EDGE) Radio Access Network (GERAN) basically support CS calls. Terrestrial Radio Access Network (UTRAN) of Universal Mobile Telecommunications System (UMTS) based on GSM supports IMS-based multimedia service as well as CS calls. For example, when a dual-mode terminal capable of accessing GERAN and UTRAN is connected to a CS call in a plane GERAN area and moves to a UTRAN area at handover, the UE can concurrently use the CS call and an enhanced PS service including messaging or file transfer.
When the state of the UE connected to the other peer entity changes as in the above case, services available to the participating users may also be changed. However, there is no specified method of notifying the participating users (i.e. entities) of the services now available.
As an associated conventional technique, there is a method of exchanging information indicating whether a service is available when a connection starts. Specifically, information indicating the radio states of participating users is exchanged between the users during call setup in CSI service. The CSI service uses a CS call for voice call and an IMS session for an enhanced PS service including messaging or file transfer. A CSI terminal and a CS/PS dual-mode terminal can support the CSI service. As described above, since the CSI service is implemented over both a CS network and a PS network (including an IMS domain), it is available in a Dual Transfer Mode (DTM) GERAN or UTRAN area. The radio capability of the area where the UE is located is equivalent to the service availability of the area in the CSI service.
FIG. 1 is a diagram illustrating a signal flow for a radio capability exchange procedure for a CSI service. Both a UE 100 (UE-A) and a UE 110 (UE-B) support the CSI service or a CS/PS dual mode. UE-A accesses an IMS core network 104 (IMS core network-A) via a CS domain 102 (CS domain-A), and UE-B accesses an IMS core network 106 (IMS core network-B) via a CS domain 108 (CS domain-B).
Referring to FIG. 1, UE-A sends information about the current radio environment of the area where UE-A is located in a SETUP message for a CS call toward UE-B in step 112. CS domain-A to which UE-A is connected sends an Initial Address Message (IAM) message including the current radio environment information to CS domain-B to which UE-B is connected in step 114. CS domain-B sends a SETUP message including the current radio environment information to UE-B in step 116. UE-B stores the current radio environment information with respect to UE-A. In step 118, UE-B sends a CONNECT message including the current radio environment information of the area where UE-B is located toward UE-A in step 118. CS domain-B sends the current radio environment information in a CON message to CS domain-A in step 120 and CS domain-A sends the current radio environment information in a CONNECT message to UE-A in step 122. UE-A also stores the current radio environment information with respect to UE-B.
In this way, both UEs get knowledge of the radio capabilities of their current areas, in other words available CSI services. However, when the state of one UE is changed after call setup, for example as occurs in handover, the other participating users in the connection are not aware that the services available have changed. Consequently, even when a PS service is available, the users are not aware and the PS service is not provided, thus the users' demand is not fulfilled.
Accordingly, there is a need for an improved method and apparatus for notifying of a change in service information according to a state in a wireless terminal.